Qt UDP通信QUdpSocket简介及案例详解

1. UDP通信概述

   UDP是无连接、不可靠、面向数据报（datagram）的协议，可以应用于对可靠性要求不高的场合。与TCP通信不同，UDP通信无需预先建立持久的socket连接，UDP每次发送数据报都需要指定目标地址和端口。

   QUdpSocket以数据报传输数据，而不是以连续的数据流。发送数据报使用函数         QUdpSocket::writeDatagram()，数据报的长度一般少于512字节，每个数据报包含发送者和接收者的IP地址和端口等信息。
     UDP数据接收，首先要使用QUdpSocket::bind()绑定一个端口，绑定端口后，socket的状态会变为已绑定状态“BoundState”。

当有数据报传入时，QudpSocket会自动发射readyRead()信号，在其槽函数中使用QUdpSocket::readDatagram()进行数据读取。abort()为解除绑定，解除后socket状态变为未连接状态“UnconnectedState”。

2. UDP消息传送的三种模式

单播模式（unicast）：一个UDP客户端发送数据报到指定地址和端口的另一UDP客户端，是一对一的数据传输。

广播模式（broadcast）：一个UDP客户端发出的数据报，在同一网络范围内其他所有的UDP客户端都可以收到。QUdpSocket支持IPv4广播。需要在数据报中指定接收端地址为QHostAddress::Broadcast，一般的广播地址是255.255.255.255。

组播模式（multicast）：UDP客户端加入到另一个组播IP地址的多播组，成员向组播地址发送的数据报，其加入组播的所有成员都可以接收到，类似于QQ群功能。QUdpSocket::joinMulticastGroup()函数实现加入多播组的功能。

QUdpSocket::leaveMulticastGroup()函数实现

在单播、广播和多播模式下，UDP程序都是对等的，不像TCP通信分为客户端和服务端。
TCP通信只有单播模式。UDP通信虽然不能保证数据传输的准确性，但是具有灵活性，一般的即时通信软件都是基于UDP通信的。

3. QUdpSocket类的接口函数

bool bind(quint16 port = 0)  为UDP通信绑定一个端口

qint64 writeDatagram(QByteArray& datagram, QHostAddress& host, quint16 port) 向目标地址和端口的UDP客户端发送数据报，返回成功发送的字节数，数据报的长度一般不超过512字节。

bool hasPendingDatagrams()     当至少有一个数据报需要读取时，返回true

qint64 pendingDatagramSize()    返回第一个待读取的数据报的大小

qint64 readDatagram(char* data, qint64 maxSize) 读取一个数据报，返回成功读取的字节数

qint64 readDatagram(char* data, qint64 maxSize, QHostAddress* address, quint16* port) 读取一个数据报，返回成功读取的字节数。发送方的主机地址和端口存储在*address和*port中(除非指针为0)

bool joinMulticastGroup(QHostAddress& groupAddress)      加入一个多播组

bool leaveMulticastGroup(QHostAddress& groupAddress)    离开一个多播组

void abort() 终止当前连接并重置套接字。通常在析构函数中写入。与disconnectFromHost()不同，该函数立即关闭套接字，丢弃写入缓冲区中的任何挂起数据。
原文链接：https://blog.csdn.net/WL0616/article/details/129050373

4.UDP对话小案例

实现发送和接收端互相发信息，类似QQ  (界面使用UI设计)

4.1.接收端

receiver.h

#ifndef RECESIVER_H
#define RECESIVER_H

#include <QWidget>
#include <QUdpSocket>
QT_BEGIN_NAMESPACE
namespace Ui { class Recesiver; }
QT_END_NAMESPACE

class Recesiver : public QWidget
{
    Q_OBJECT

public:
    Recesiver(QWidget *parent = nullptr);
    ~Recesiver();

private slots:
    void on_pushButton_2_clicked(); //启动槽函数
    void start();
    void on_pushButton_clicked();

private:
    Ui::Recesiver *ui;
    QUdpSocket *receiver;
};
#endif // RECESIVER_H

receiver.cpp

#include "recesiver.h"
#include "ui_recesiver.h"

Recesiver::Recesiver(QWidget *parent)
    : QWidget(parent)
    , ui(new Ui::Recesiver)
{
    ui->setupUi(this);
    setWindowTitle(QStringLiteral("接收端"));
    ui->lineEdit->setText("127.0.0.1");
    receiver =new QUdpSocket(this);
}

Recesiver::~Recesiver()
{
    delete ui;
}

//接收信息
 void Recesiver::start()
 {
    QByteArray datagram;
    datagram.resize(receiver->pendingDatagramSize()); //接收到的数据的长度
    receiver->readDatagram(datagram.data(),datagram.size());
    ui->textEdit->append(QStringLiteral("对方：")+datagram);
 }

//启动按钮（发送端发送信息给接收端）
void Recesiver::on_pushButton_2_clicked()
{
   receiver->bind(ui->lineEdit_2->text().toInt());//设置端口号将其转为整型
   connect(receiver,&QUdpSocket::readyRead,this,[&](){start();});
   ui->pushButton_2->setEnabled(false);
   ui->lineEdit_2->setEnabled(false);
}

//发送按钮（接收端发送信息给发送端）
void Recesiver::on_pushButton_clicked()
{
    QByteArray datagram=ui->textEdit_2->toPlainText().toUtf8();  //在输入端输入发送的内容
    receiver->writeDatagram(datagram.data(),datagram.size(),QHostAddress(ui->lineEdit->text()),ui->lineEdit_3->text().toInt());
    //qint64 writeDatagram(const char *data, qint64 len, const QHostAddress &host, quint16 port);
    //发送数据，大小，发送主机的ip,发送主机的端口号
    ui->textEdit->append(QStringLiteral("本机：")+ui->textEdit_2->toPlainText());//发送信息的具体内容在发送端的聊天记录里能体现
    ui->textEdit_2->clear();
}

4.2发送端

sender.h

#ifndef SENDER_H
#define SENDER_H
#include <QWidget>
#include <QUdpSocket>
QT_BEGIN_NAMESPACE
namespace Ui { class Sender; }
QT_END_NAMESPACE

class Sender : public QWidget
{
    Q_OBJECT

public:
    Sender(QWidget *parent = nullptr);
    ~Sender();
    void  start2();
private slots:
    void on_pushButton_clicked();

private:
    Ui::Sender *ui;
    QUdpSocket *sender;
};
#endif // SENDER_H

sender.cpp

#include "sender.h"
#include "ui_sender.h"

Sender::Sender(QWidget *parent)
    : QWidget(parent)
    , ui(new Ui::Sender)
{
    ui->setupUi(this);
    sender=new QUdpSocket(this);
    setWindowTitle(QStringLiteral("发送端"));

    //sender
    ui->lineEdit_3->setText("888");
    sender->bind(ui->lineEdit_3->text().toInt());//绑定端口号

    connect(sender,&QUdpSocket::readyRead,this,[&](){start2();});
    //start2();
}

void Sender::start2()
{
    QByteArray datagram;
    datagram.resize(sender->pendingDatagramSize()); //接收到的数据的长度
    sender->readDatagram(datagram.data(),datagram.size());
    ui->textEdit->append(QStringLiteral("对方：")+datagram);
}


Sender::~Sender()
{
    delete ui;
}


//发送按钮 发送信息给接收端
void Sender::on_pushButton_clicked()
{
   QByteArray datagram=ui->textEdit_2->toPlainText().toUtf8();  //在输入端输入发送的内容
   sender->writeDatagram(datagram.data(),datagram.size(),QHostAddress(ui->lineEdit->text()),ui->lineEdit_2->text().toInt());
   //qint64 writeDatagram(const char *data, qint64 len, const QHostAddress &host, quint16 port);
   //发送数据，大小，发送主机的ip,发送主机的端口号
   ui->textEdit->append(QStringLiteral("本机：")+ui->textEdit_2->toPlainText());//发送信息的具体内容在发送端的聊天记录里能体现
   ui->textEdit_2->clear();

}

结果：

（ps：对话有点搞笑，哈哈哈）

5.4. UDP单播和广播代码示例

4.1 测试说明

  本实例实现UDP通信的单播和广播。两个实例可以运行在同一台计算机上，也可以运行在不同的计算机上。
这里的两个实例是运行在同一台计算机上，需要注意，在同一台计算机上运行时，两个实例需要绑定不同的端口。例如实例A绑定端口1600，实例B绑定端口3200，实例A向实例B发送数据报时，需要指定实例B的端口，这样实例B才能收到数据。
如果两个实例在不同的计算机上运行，则端口可以一样，因为IP地址不同了，不会导致绑定时发生冲突。一般的UDP通信程序都是在不同的计算机上运行的，约定一个固定的端口作为通信端口。

4.2主要程序

用UI设计器件和代码化UI分别设计

ui设计器设计：

.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QLabel>
#include <QAbstractSocket>
#include <QUdpSocket>
QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = nullptr);
    ~MainWindow();
    void   handleEvents();                                                 // 信号与槽处理

private:
    Ui::MainWindow *ui;

    QUdpSocket *udpScoket;
    QLabel *labstateScoket;   //Scoket状态栏标签
    QString  getLocalIp();  //获取本机的IP地址
private slots:

    void slotActBindPort();   //绑定端口
    void slotActUnbindPort(); //解除端口
    void slotActClearText();  //清空文本框
    void slotActQuit();       //退出

    void slotSocketReadyRead();  //读取socket传入的数据
    void slotSocketStateChanged(QAbstractSocket::SocketState socketState);

    void on_pushButton_clicked(); //发送信息
    void on_pushButton_2_clicked(); //广播信息
};
#endif // MAINWINDOW_H

.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QTextEdit>
#include <QMessageBox>
#include <QHostInfo>

#include <QAction>
#include <QPushButton>
MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);

    QString localIP = getLocalIp(); //获取本机的IP地址
    this->setWindowTitle(this->windowTitle() + "---IP:" + localIP);

    ui->comboBox->addItem(localIP); //在目标地址中添加IP
    udpScoket = new QUdpSocket(this);

    //状态栏
    labstateScoket = new QLabel(QStringLiteral("socket状态："), this);
    labstateScoket->setMinimumWidth(150);
    ui->statusBar->addWidget(labstateScoket);
    handleEvents();

    ui->spinBox->setMinimum(1);     //设置绑定端口的最大最小值和当前的端口值
    ui->spinBox->setMaximum(65535);
    ui->spinBox->setValue(1600);

    ui->spinBox_2->setMinimum(1);   //设置目标端口的最大最小值和当前的端口值
    ui->spinBox_2->setMaximum(65535);
    ui->spinBox_2->setValue(3200);

}

MainWindow::~MainWindow()
{
    udpScoket->abort();
    delete udpScoket;
    udpScoket = nullptr;
    delete ui;
}


// 信号与槽处理
void MainWindow::handleEvents()
{

    connect(ui->action, &QAction::triggered, this, &MainWindow::slotActBindPort );
    connect(ui->action_2, &QAction::triggered, this, &MainWindow::slotActUnbindPort);
    connect(ui->action_3, &QAction::triggered, this, &MainWindow::slotActClearText);
    connect(ui->action_4, &QAction::triggered, this, &MainWindow::slotActQuit);

    connect(ui->pushButton, &QPushButton::clicked, this, &MainWindow::on_pushButton_clicked);
    connect(ui->pushButton_2, &QPushButton::clicked, this, &MainWindow::on_pushButton_2_clicked);

    connect(udpScoket, &QUdpSocket::stateChanged, this, &MainWindow::slotSocketStateChanged);
    connect(udpScoket, &QUdpSocket::readyRead, this, &MainWindow::slotSocketReadyRead);

}


QString MainWindow::getLocalIp()
{
    QString hostName = QHostInfo::localHostName();//获取本机主机名
    QHostInfo hostInfo = QHostInfo::fromName(hostName);  //返回主机名的IP地址

    QString localIP = "";
    QList<QHostAddress> addrList = hostInfo.addresses();   //主机IP地址列表

    if (!addrList.isEmpty())
    {
        for (int i = 0; i < addrList.size(); i++)
        {
            QHostAddress addr = addrList.at(i);
            if (QAbstractSocket::IPv4Protocol == addr.protocol())
            {
                localIP = addr.toString();
                break;
            }
        }
    }
    return localIP;
}


//绑定端口
void MainWindow::slotActBindPort()
{
    quint16 port=ui->spinBox->value();   //绑定本机UDp端口
    if(udpScoket->bind(port))
    {
        ui->textEdit->append(QStringLiteral("**已经绑定成功"));
        ui->textEdit->append(QStringLiteral("**绑定端口：")+QString::number(udpScoket->localPort()));
        ui->action->setEnabled(false); //开始绑定失效
        ui->action_2->setEnabled(true);//解除绑定使能
    }
    else
        ui->textEdit->append(QStringLiteral("绑定失败"));
}

//解除端口
void MainWindow::slotActUnbindPort()
{

    udpScoket->abort();//解除绑定
    ui->action->setEnabled(true); //开始绑定失效
    ui->action_2->setEnabled(false);//解除绑定使能
    ui->textEdit->append(QStringLiteral("**已经解除绑定"));

}

//清空文本框
void MainWindow::slotActClearText()
{
    ui->textEdit->clear();
}


//退出
void MainWindow::slotActQuit()
{
    QMessageBox::StandardButton button = QMessageBox::question(this, "", QStringLiteral("是否要退出？"));
    if (button == QMessageBox::StandardButton::Yes)
        this->close();
}

//读取socket传入的数据
void MainWindow::slotSocketReadyRead()
{
    while(udpScoket->hasPendingDatagrams()) //当有数据传入数据报
     {
       QByteArray  datagtam;
       datagtam.resize(udpScoket->pendingDatagramSize());//读取数据报大小

       QHostAddress peerAddr;  //在已连接的状态下，返回对方的socket的地址
       quint16 peerPort;       //在已连接的状态下，返回对方的socket的端口

       udpScoket->readDatagram(datagtam.data(),datagtam.size(),&peerAddr,&peerPort);//读取数据报的内容
       //qint64 readDatagram(char *data, qint64 maxlen, QHostAddress *host = nullptr, quint16 *port = nullptr);

       QString str=datagtam.data();
       QString  peer="[From "+peerAddr.toString()+":"+QString::number(peerPort)+"]";
       ui->textEdit->append( peer + str);
     }
}

 //状态栏显示Socket变化情况
void MainWindow::slotSocketStateChanged(QAbstractSocket::SocketState socketState)
{
    switch (socketState)
    {
            case QAbstractSocket::UnconnectedState: labstateScoket->setText(QStringLiteral("socket状态：UnconnectedState")); break;
            case QAbstractSocket::HostLookupState: labstateScoket->setText(QStringLiteral("socket状态：HostLookupState")); break;
            case QAbstractSocket::ConnectingState: labstateScoket->setText(QStringLiteral("socket状态：ConnectingState")); break;
            case QAbstractSocket::ConnectedState: labstateScoket->setText(QStringLiteral("socket状态：ConnectedState")); break;
            case QAbstractSocket::BoundState: labstateScoket->setText(QStringLiteral("socket状态：BoundState")); break;
            case QAbstractSocket::ClosingState: labstateScoket->setText(QStringLiteral("socket状态：ClosingState")); break;
            default: break;
     }

}


//发送信息
void MainWindow::on_pushButton_clicked()
{
        QString msg = ui->lineEdit->text(); //发送信息
        QByteArray str = msg.toUtf8();

        QString targetIp = ui->comboBox->currentText();  //目标IP就是主机地址的ip
        QHostAddress targetAddr(targetIp);
        quint16 targetPort = ui->spinBox_2->value();  //目标端口

        udpScoket->writeDatagram(str, targetAddr, targetPort);//发出数据报
        ui->textEdit->append("[out] " + msg);
        ui->lineEdit->clear();
        ui->lineEdit->setFocus();

}
//广播信息
void MainWindow::on_pushButton_2_clicked()
{
      quint16 targetPort = ui->spinBox_2->value();  //目标端口
      QString msg=ui->lineEdit->text();

      QByteArray str = msg.toUtf8();
      udpScoket->writeDatagram(str, QHostAddress::Broadcast, targetPort);//发出数据报
      ui->textEdit->append("[broadcast] " + msg);
      ui->lineEdit->clear();
      ui->lineEdit->setFocus();

}

代码化：

.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QAction>
#include <QComboBox>
#include <QGridLayout>
#include <QHBoxLayout>
#include <QHostInfo>
#include <QLabel>
#include <QLineEdit>
#include <QMainWindow>
#include <QMessageBox>
#include <QPlainTextEdit>
#include <QPushButton>
#include <QSpinBox>
#include <QUdpSocket>
#include <QVBoxLayout>

namespace Ui {
    class MainWindow;
}

class MainWindow : public QMainWindow {
    Q_OBJECT

public:
    explicit MainWindow(QWidget* parent = 0);
    ~MainWindow();

private slots:
    void slotActBindPort();
    void slotActUnbindPort();
    void slotActClearText();
    void slotActQuit();
    void slotSocketStateChanged(QAbstractSocket::SocketState socketState);
    void slotBtnSend();
    void slotBtnBroad();
    void slotSocketReadyRead();  //读取socket传入的数据

private:
    Ui::MainWindow* ui;

    QAction* m_pActBindPort;
    QAction* m_pActUnbindPort;
    QAction* m_pActClearText;
    QAction* m_pActQuit;
    QWidget* m_pCentralWidget;
    QLabel* m_pLabBindPort;
    QLabel* m_PLabTargetAddr;
    QLabel* m_pLabTargetPort;
    QSpinBox* m_pSpinBindPort;
    QComboBox* m_pComboTargetAddr;
    QSpinBox* m_pSpinTargetPort;
    QLineEdit* m_pLineEdit;
    QPushButton* m_pBtnSend;
    QPushButton* m_pBtnBroad;
    QPlainTextEdit* m_pPlainText;
    QLabel* m_pLabState;
    QUdpSocket* m_pUdpSocket;

    QString getLocalIP();
};

#endif  // MAINWINDOW_H

.cpp

#include "mainwindow.h"
#include <QToolBar>
#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget* parent) : QMainWindow(parent), ui(new Ui::MainWindow) {
    ui->setupUi(this);
    //this->setWindowIcon(QIcon(":/new/prefix1/res/TitleIcon.png"));
    this->setWindowTitle(QStringLiteral("UDP Send/Receiver"));

    //工具栏
    ui->toolBar->setToolButtonStyle(Qt::ToolButtonTextBesideIcon);
    m_pActBindPort = new QAction(QIcon(":/new/Check.png"), QStringLiteral("绑定端口"), this);
    m_pActUnbindPort = new QAction(QIcon(":/new/Break.png"), QStringLiteral("结束绑定"), this);
    m_pActClearText = new QAction(QIcon(":/new/remove.png"), QStringLiteral("清空文本"), this);
    m_pActQuit = new QAction(QIcon(":/new/back.png"), QStringLiteral("退出"), this);
    ui->toolBar->addAction(m_pActBindPort);
    ui->toolBar->addAction(m_pActUnbindPort);
    ui->toolBar->addSeparator();
    ui->toolBar->addAction(m_pActClearText);
    ui->toolBar->addSeparator();
    ui->toolBar->addAction(m_pActQuit);

    //界面布局
    m_pCentralWidget = new QWidget(this);

    QHBoxLayout* HLay1 = new QHBoxLayout;
    m_pLabBindPort = new QLabel(QStringLiteral("绑定端口"), m_pCentralWidget);
    m_pSpinBindPort = new QSpinBox(m_pCentralWidget);
    m_pSpinBindPort->setMinimum(1);
    m_pSpinBindPort->setMaximum(65535);
    m_pSpinBindPort->setValue(3200);
    m_PLabTargetAddr = new QLabel(QStringLiteral("目标地址"), m_pCentralWidget);
    m_pComboTargetAddr = new QComboBox(m_pCentralWidget);
    m_pLabTargetPort = new QLabel(QStringLiteral("目标端口"), m_pCentralWidget);
    m_pSpinTargetPort = new QSpinBox(m_pCentralWidget);
    m_pSpinTargetPort->setMinimum(1);
    m_pSpinTargetPort->setMaximum(65535);
    m_pSpinTargetPort->setValue(1600);
    HLay1->addWidget(m_pLabBindPort, 1, Qt::AlignRight);
    HLay1->addWidget(m_pSpinBindPort, 2);
    HLay1->addWidget(m_PLabTargetAddr, 1, Qt::AlignRight);
    HLay1->addWidget(m_pComboTargetAddr, 4);
    HLay1->addWidget(m_pLabTargetPort, 1, Qt::AlignRight);
    HLay1->addWidget(m_pSpinTargetPort, 2);

    QHBoxLayout* HLay2 = new QHBoxLayout;
    m_pLineEdit = new QLineEdit(m_pCentralWidget);
    m_pBtnSend = new QPushButton(QStringLiteral("发送消息"), m_pCentralWidget);
    m_pBtnBroad = new QPushButton(QStringLiteral("广播消息"), m_pCentralWidget);
    HLay2->addWidget(m_pLineEdit);
    HLay2->addWidget(m_pBtnSend);
    HLay2->addWidget(m_pBtnBroad);

    QVBoxLayout* VLay = new QVBoxLayout(m_pCentralWidget);  //主布局必须设置parent，否则不会显示布局
    // QVBoxLayout* VLay = new QVBoxLayout();
    VLay->addLayout(HLay1);
    VLay->addLayout(HLay2);
    m_pPlainText = new QPlainTextEdit(m_pCentralWidget);
    VLay->addWidget(m_pPlainText);

    this->setCentralWidget(m_pCentralWidget);
    this->setLayout(VLay);  //设置为窗体的主布。在指定了主布局的parent之后，这句话可有可无

    QString localIP = getLocalIP();
    this->setWindowTitle(this->windowTitle() + "---IP:" + localIP);
    m_pComboTargetAddr->addItem(localIP);
    m_pUdpSocket = new QUdpSocket(this);

    //状态栏
    m_pLabState = new QLabel(QStringLiteral("socket状态："), this);
    m_pLabState->setMinimumWidth(150);
    ui->statusbar->addWidget(m_pLabState);

    // connect
    connect(m_pActBindPort, &QAction::triggered, this, &MainWindow::slotActBindPort);
    connect(m_pActUnbindPort, &QAction::triggered, this, &MainWindow::slotActUnbindPort);
    connect(m_pActClearText, &QAction::triggered, this, &MainWindow::slotActClearText);
    connect(m_pActQuit, &QAction::triggered, this, &MainWindow::slotActQuit);
    connect(m_pBtnSend, &QPushButton::clicked, this, &MainWindow::slotBtnSend);
    connect(m_pBtnBroad, &QPushButton::clicked, this, &MainWindow::slotBtnBroad);
    connect(m_pUdpSocket, &QUdpSocket::stateChanged, this, &MainWindow::slotSocketStateChanged);
    connect(m_pUdpSocket, &QUdpSocket::readyRead, this, &MainWindow::slotSocketReadyRead);
}

MainWindow::~MainWindow() {
    //m_pUdpSocket->abort();
    //delete m_pUdpSocket;
    //m_pUdpSocket = nullptr;
    delete ui;
}

void MainWindow::slotActBindPort()
{
    quint16 port = m_pSpinBindPort->value();  //本机UDP端口
    if (m_pUdpSocket->bind(port)) {
        m_pPlainText->appendPlainText(QStringLiteral("**已成功绑定"));
        m_pPlainText->appendPlainText(QStringLiteral("绑定端口：") + QString::number(m_pUdpSocket->localPort()));

        //使能
        m_pActBindPort->setEnabled(false);
        m_pActUnbindPort->setEnabled(true);
    } else {
        m_pPlainText->appendPlainText(QStringLiteral("绑定失败"));
    }
}

void MainWindow::slotActUnbindPort() {
    m_pUdpSocket->abort();  //解除绑定
    m_pPlainText->appendPlainText(QStringLiteral("**已解除绑定"));

    m_pActBindPort->setEnabled(true);
    m_pActUnbindPort->setEnabled(false);
}

void MainWindow::slotActClearText() { m_pPlainText->clear(); }

void MainWindow::slotActQuit() {
    QMessageBox::StandardButton button = QMessageBox::question(this, "", QStringLiteral("是否要退出？"));
    if (button == QMessageBox::StandardButton::Yes)
        this->close();
}

void MainWindow::slotSocketStateChanged(QAbstractSocket::SocketState socketState) {
    switch (socketState)
    {
            case QAbstractSocket::UnconnectedState: m_pLabState->setText(QStringLiteral("socket状态：UnconnectedState")); break;
            case QAbstractSocket::HostLookupState: m_pLabState->setText(QStringLiteral("socket状态：HostLookupState")); break;
            case QAbstractSocket::ConnectingState: m_pLabState->setText(QStringLiteral("socket状态：ConnectingState")); break;
            case QAbstractSocket::ConnectedState: m_pLabState->setText(QStringLiteral("socket状态：ConnectedState")); break;
            case QAbstractSocket::BoundState: m_pLabState->setText(QStringLiteral("socket状态：BoundState")); break;
            case QAbstractSocket::ClosingState: m_pLabState->setText(QStringLiteral("socket状态：ClosingState")); break;
            default: break;
     }

}

void MainWindow::slotBtnSend()
{
    QString msg = m_pLineEdit->text();
    QByteArray str = msg.toUtf8();
    QString targetIp = m_pComboTargetAddr->currentText();  //目标IP
    QHostAddress targetAddr(targetIp);
    quint16 targetPort = m_pSpinTargetPort->value();  //目标端口
    m_pUdpSocket->writeDatagram(str, targetAddr, targetPort);
    m_pPlainText->appendPlainText("[out] " + msg);
    m_pLineEdit->clear();
    m_pLineEdit->setFocus();

}

void MainWindow::slotBtnBroad()
{
    QString msg = m_pLineEdit->text();
    QByteArray str = msg.toUtf8();
    quint16 targetPort = m_pSpinTargetPort->value();
    m_pUdpSocket->writeDatagram(str, QHostAddress::Broadcast, targetPort);
    m_pPlainText->appendPlainText("[out] " + msg);
    m_pLineEdit->clear();
    m_pLineEdit->setFocus();



}

void MainWindow::slotSocketReadyRead()
{
    while (m_pUdpSocket->hasPendingDatagrams())
    {
        QByteArray dataGram;
        dataGram.resize(m_pUdpSocket->pendingDatagramSize());
        QHostAddress peerAddress;
        quint16 peerPort;
        m_pUdpSocket->readDatagram(dataGram.data(), dataGram.size(), &peerAddress, &peerPort);
        QString str = dataGram.data();
        QString peer = "[From " + peerAddress.toString() + ":" + QString::number(peerPort) + "]";
        m_pPlainText->appendPlainText(peer + str);
    }
}

QString MainWindow::getLocalIP() {
    QString hostName = QHostInfo::localHostName();
    QHostInfo hostInfo = QHostInfo::fromName(hostName);
    QString localIP = "";
    QList<QHostAddress> addrList = hostInfo.addresses();
    if (!addrList.isEmpty()) {
        for (int i = 0; i < addrList.size(); i++) {
            QHostAddress addr = addrList.at(i);
            if (QAbstractSocket::IPv4Protocol == addr.protocol()) {
                localIP = addr.toString();
                break;
            }
        }
    }
    return localIP;
}

结果： 

 发现自己用UI设计时，发送信息总会出现两个发送信号，并且有一个是空白的，暂时还没有找到问题所在之处，嘤嘤嘤~(/≧▽≦)/

5. UDP组播代码示例

5.1 组播的特性

组播报文的目的地址使用D类IP地址，D类地址不能出现在IP报文的地址字段。用同一个IP多播地址接收多播数据报的所有主机构成一个组，称为多播组（或组播组）。所有的信息接收者都加入一个组内，并且一旦加入后，流向组地址的数据报立即开始向接收者传输，组中的所有的成员都能接收到数据报。组中的成员是动态的，主机可以在任何人时间加入和离开组。

关于组播IP地址，有以下约定：

224.0.0.0 ~ 224.0.0.255   为预留的组播地址（永久组地址），地址224.0.0.0保留不做分配，其他地址供路由协议使用。
224.0.1.0 ~ 224.0.1.255   是公用组播地址，可以用于Internet。
224.0.2.0 ~ 238.255.255.255     为用户可用的组播地址（临时组地址），全网范围内有效。
239.0.0.0 ~ 239.255.255.255     为本地管理组播地址，仅在特定的本地范围内有效。所以，若是在家庭或办公室局域网内测试UDP组播功能，可以使用这些IP。
原文链接：https://blog.csdn.net/WL0616/article/details/129050373

5.2主要程序 

.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QAction>
#include <QComboBox>
#include <QHBoxLayout>
#include <QHostInfo>
#include <QLabel>
#include <QLineEdit>
#include <QMainWindow>
#include <QMessageBox>
#include <QPlainTextEdit>
#include <QPushButton>
#include <QRegExp>
#include <QSpinBox>
#include <QUdpSocket>
#include <QVBoxLayout>

namespace Ui {
    class MainWindow;
}

class MainWindow : public QMainWindow {
    Q_OBJECT

public:
    explicit MainWindow(QWidget* parent = 0);
    ~MainWindow();

private slots:
    void slotActJoinMulti();
    void slotActLeaveMulti();
    void slotActClearText();
    void slotActQuit();
    void slotSocketStateChanged(QAbstractSocket::SocketState socketState);
    void slotBtnMultiMsg();
    void slotReadyRead();

private:
    Ui::MainWindow* ui;

    QAction* m_pActJoinMulti;
    QAction* m_pActLeaveMulti;
    QAction* m_pActClearText;
    QAction* m_pActQuit;
    QWidget* m_pCentralWidget;
    QLabel* m_pLabPort;
    QLabel* m_pLabAddr;
    QSpinBox* m_pSpinPort;
    QComboBox* m_pComboAddr;
    QLineEdit* m_pLineEdit;
    QPushButton* m_pBtnSendMulti;
    QPlainTextEdit* m_pPlainText;
    QLabel* m_pLabState;
    QUdpSocket* m_pUdpSocket;
    QHostAddress m_multicastAddr;

    QString getLocalIP();
};

#endif  // MAINWINDOW_H

.cpp

#include "mainwindow.h"

#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget* parent) : QMainWindow(parent), ui(new Ui::MainWindow) {
    ui->setupUi(this);
    this->setWindowTitle(QStringLiteral("UDP Multicast"));

    //工具栏
    ui->mainToolBar->setToolButtonStyle(Qt::ToolButtonTextBesideIcon);
    m_pActJoinMulti = new QAction(QIcon(":/new/prefix1/res/添加群组.png"), QStringLiteral("加入组播"), this);
    m_pActLeaveMulti = new QAction(QIcon(":/new/prefix1/res/退出群组.png"), QStringLiteral("退出组播"), this);
    m_pActClearText = new QAction(QIcon(":/new/prefix1/res/清空.png"), QStringLiteral("清空文本"), this);
    m_pActQuit = new QAction(QIcon(":/new/prefix1/res/退出.png"), QStringLiteral("退出"), this);
    ui->mainToolBar->addAction(m_pActJoinMulti);
    ui->mainToolBar->addAction(m_pActLeaveMulti);
    ui->mainToolBar->addSeparator();
    ui->mainToolBar->addAction(m_pActClearText);
    ui->mainToolBar->addSeparator();
    ui->mainToolBar->addAction(m_pActQuit);

    //界面布局
    m_pCentralWidget = new QWidget(this);
    m_pLabPort = new QLabel(QStringLiteral("组播端口"), m_pCentralWidget);
    m_pSpinPort = new QSpinBox(m_pCentralWidget);
    m_pSpinPort->setMinimum(1);
    m_pSpinPort->setMaximum(65535);
    m_pSpinPort->setValue(3200);
    m_pLabAddr = new QLabel(QStringLiteral("组播地址"), m_pCentralWidget);
    m_pComboAddr = new QComboBox(m_pCentralWidget);
    m_pComboAddr->setEditable(true);  //下拉框可编辑输入
    m_pComboAddr->addItem("239.0.0.1");
    // 正则匹配 D类IP：224.0.0.0~239.255.255.255
    // .必须使用转义字符\，否则.会匹配任意字符
    // C++中"\"在字符串中表示要用"\\"
    // 是 - 不是 ~ ； 是[0-9]不是[0~9]
    QRegExp regExp("^(22[4-9]|23[0-9])(\\.((\\d)|([1-9]\\d)|(1\\d{2})|(2[0-4]\\d)|(25[0-5]))){3}$");
    QValidator* pValidator = new QRegExpValidator(regExp, this);
    m_pComboAddr->setValidator(pValidator);
    QHBoxLayout* HLay1 = new QHBoxLayout();
    HLay1->addWidget(m_pLabPort, 1, Qt::AlignRight);
    HLay1->addWidget(m_pSpinPort, 1);
    HLay1->addWidget(m_pLabAddr, 1, Qt::AlignRight);
    HLay1->addWidget(m_pComboAddr, 2);
    m_pLineEdit = new QLineEdit(m_pCentralWidget);
    m_pBtnSendMulti = new QPushButton(QStringLiteral("组播消息"), m_pCentralWidget);
    QHBoxLayout* HLay2 = new QHBoxLayout();
    HLay2->addWidget(m_pLineEdit, 4);
    HLay2->addWidget(m_pBtnSendMulti, 1);
    m_pPlainText = new QPlainTextEdit(m_pCentralWidget);
    QVBoxLayout* VLay = new QVBoxLayout(m_pCentralWidget);
    VLay->addLayout(HLay1);
    VLay->addLayout(HLay2);
    VLay->addWidget(m_pPlainText);
    this->setCentralWidget(m_pCentralWidget);
    this->setLayout(VLay);

    //状态栏
    m_pLabState = new QLabel(QStringLiteral("socket状态："), this);
    m_pLabState->setMinimumWidth(150);
    ui->statusBar->addWidget(m_pLabState);

    QString str = getLocalIP();
    this->setWindowTitle(this->windowTitle() + "---IP:" + str);

    m_pUdpSocket = new QUdpSocket(this);
    m_pUdpSocket->setSocketOption(QAbstractSocket::MulticastTtlOption, 1);

    // connect
    connect(m_pActJoinMulti, &QAction::triggered, this, &MainWindow::slotActJoinMulti);
    connect(m_pActLeaveMulti, &QAction::triggered, this, &MainWindow::slotActLeaveMulti);
    connect(m_pActClearText, &QAction::triggered, this, &MainWindow::slotActClearText);
    connect(m_pActQuit, &QAction::triggered, this, &MainWindow::slotActQuit);
    connect(m_pUdpSocket, &QUdpSocket::stateChanged, this, &MainWindow::slotSocketStateChanged);
    connect(m_pBtnSendMulti, &QPushButton::clicked, this, &MainWindow::slotBtnMultiMsg);
    connect(m_pUdpSocket, &QUdpSocket::readyRead, this, &MainWindow::slotReadyRead);
}

MainWindow::~MainWindow() { delete ui; }

void MainWindow::slotActJoinMulti() {
    QString ip = m_pComboAddr->currentText();
    m_multicastAddr = QHostAddress(ip);
    quint16 multicastPort = m_pSpinPort->value();
    if (m_pUdpSocket->bind(QHostAddress::AnyIPv4, multicastPort, QUdpSocket::ShareAddress)) {
        m_pUdpSocket->joinMulticastGroup(m_multicastAddr);  //加入多播组
        m_pPlainText->appendPlainText("**加入组播成功");
        m_pPlainText->appendPlainText("**组播地址IP：" + ip);
        m_pPlainText->appendPlainText("**绑定端口：" + QString::number(multicastPort));
        m_pActJoinMulti->setEnabled(false);
        m_pActLeaveMulti->setEnabled(true);
        m_pComboAddr->setEditable(false);
    } else {
        m_pPlainText->appendPlainText("**绑定端口失败");
    }
}

void MainWindow::slotActLeaveMulti() {
    m_pUdpSocket->leaveMulticastGroup(m_multicastAddr);  //退出组播
    m_pUdpSocket->abort();                               //解除绑定
    m_pActJoinMulti->setEnabled(true);
    m_pActLeaveMulti->setEnabled(false);
    m_pComboAddr->setEnabled(true);
    m_pComboAddr->setEditable(true);
    m_pPlainText->appendPlainText("**已退出组播，解除端口绑定");
}

void MainWindow::slotActClearText() { m_pPlainText->clear(); }

void MainWindow::slotActQuit() {
    QMessageBox::StandardButton button = QMessageBox::question(this, "", "是否退出？");
    if (QMessageBox::StandardButton::Yes == button) {
        this->close();
    }
}

void MainWindow::slotSocketStateChanged(QAbstractSocket::SocketState socketState) {
    // case并不包含所有的情况，因为没有写listening的情况，所以就需要写default
    switch (socketState) {
        case QAbstractSocket::UnconnectedState: m_pLabState->setText("socket状态：UnconnectedState"); break;
        case QAbstractSocket::HostLookupState: m_pLabState->setText("socket状态：HostLookupState"); break;
        case QAbstractSocket::ConnectingState: m_pLabState->setText("socket状态：ConnectingState"); break;
        case QAbstractSocket::ConnectedState: m_pLabState->setText("socket状态：ConnectedState"); break;
        case QAbstractSocket::BoundState: m_pLabState->setText("socket状态：BoundState"); break;
        case QAbstractSocket::ClosingState: m_pLabState->setText("socket状态：ClosingState"); break;
        default: break;
    }
}

void MainWindow::slotBtnMultiMsg() {
    QString msg = m_pLineEdit->text();
    QByteArray str = msg.toUtf8();
    quint16 multiPort = m_pSpinPort->value();
    m_pUdpSocket->writeDatagram(str, m_multicastAddr, multiPort);
    m_pPlainText->appendPlainText("[multicast] " + msg);
    m_pLineEdit->clear();
    m_pLineEdit->setFocus();
}

void MainWindow::slotReadyRead() {
    while (m_pUdpSocket->hasPendingDatagrams()) {
        QByteArray dataGram;
        dataGram.resize(m_pUdpSocket->pendingDatagramSize());
        QHostAddress peerAddr;
        quint16 peerPort;
        m_pUdpSocket->readDatagram(dataGram.data(), dataGram.size(), &peerAddr, &peerPort);
        QString str = dataGram.data();
        QString peer = "[From " + peerAddr.toString() + ":" + QString::number(peerPort) + "] ";
        m_pPlainText->appendPlainText(peer + str);
        qDebug() << m_pUdpSocket->peerAddress();
        qDebug() << m_pUdpSocket->localAddress().toString();
        qDebug() << m_pUdpSocket->localPort();
    }
}

QString MainWindow::getLocalIP() {
    QString localName = QHostInfo::localHostName();
    QHostInfo hostInfo = QHostInfo::fromName(localName);
    QList<QHostAddress> addrList = hostInfo.addresses();
    QString localIP = "";
    if (!addrList.isEmpty()) {
        for (int i = 0; i < addrList.size(); i++) {
            QHostAddress addr = addrList.at(i);
            if (QAbstractSocket::IPv4Protocol == addr.protocol()) {
                localIP = addr.toString();
                break;
            }
        }
    }
    return localIP;
}

结果： 

原文链接：https://blog.csdn.net/WL0616/article/details/129050373